Managing powdery mildew on garden and indoor plants

Whether gardening indoors or outdoors, gardeners are likely to encounter powdery mildew on one or more of their plants. First, a white powdery substance will appear on the surface of leaves, stems and flower petals. As the powdery mildew expands and covers the leaves, it blocks sunlight from reaching the leaves inhibiting photosynthesis. As the disease progresses, it develops struc­tures that enter plant cells to obtain nutrients. It usually is not fatal but severe infestations can cause plant leaves to yellow, twist and discolor and the plant may decline.

Several closely related fungi are responsible for the group of diseases called powdery mildew. Different species of powdery mildew fungi attack different plants. If the weather condi­tions are right and the various fungi are present, gardeners may find powdery mildew on a variety of plants in their land­scape or indoor garden.

Watch for powdery mildew on azaleas, crabapples, dogwoods, lilacs, photinia, roses, coral hon­eysuckle vines and other trees, shrubs and vines. Check bee­balm, dahlias, peonies, phlox, zinnias, cucumbers, squash and other susceptible plants in gar­dens. Indoors, especially dur­ing the winter, monitor African violets, begonias, ivies, jade and kalanchoes that may develop this disease.

Unlike many fungal diseas­es, powdery mildew fungi need high humidity not wet leaves to develop. Their spores also form in high humidity and are dis­tributed when the humidity is low.

Powdery mildew is more likely to occur on indoor plants growing in low light with poor air circulation and cooler tem­peratures near 70° F. Although the disease is more common in winter the disease can occur anytime these conditions exist.

Reduce the risk of powdery mildew by keeping plants healthy and avoiding overfer­tilization. Provide plants with the needed light and other preferred growing conditions. Properly space landscape plants and avoid overcrowding plants, indoors and out, to provide suf­ficient light penetration and air circulation.

Water new plantings thor­oughly and often enough to keep the roots moist. Gradually reduce the frequency to encour­age the plants to develop a ro­bust root system. Continue to water established plants thor­oughly as needed during dry weather.

With proper care and sanita­tion healthy perennials, shrubs and trees, especially those in­fected late in the growing sea­son, will return the following year.

Melinda Myers’ website is www. MelindaMyers.com.